Removing a fraction of the lignin from black liquor allows pulp and paper mills that have reached the maximum throughput of their recovery boilers to increase production proportional to the fraction of lignin removed. For example, a large paper mill recovering 30% of their lignin from black liquor allows the mill to increase the overall production rate approaching that same percentage.
Lignin is also a valuable material for production of “green chemicals.” The value of the lignin can increase even further if the lignin can be refined to a high degree by separating it effectively from ash and desulfurizing the covalently bound sulfite and sulfonate groups it acquires in the pulping process. PCT/US2013/039585 and PCT/US2013/068824 (both incorporated herein by reference for all purposes) disclose processes and methods to refine lignin to high purity by extracting it into a limited-solubility solvent and polishing the lignin in the organic phase by contacting with a strong acid cation exchange resin.